This invention relates in general to the manufacture of formed end metal products and, in particular, to a method and apparatus for making such products.
Formed end metal products are produced for a variety of applications, including truck and automobile axles, tie rods for anchoring utility poles, and sucker rods for use in well drilling applications. These products comprise a forged or machined end, such as a threaded box or pin, a hook, an eye, or other formed shape, attached to or formed on the end of any elongate metal member, such as a rod, bar or tube. The formed end may be directly forged or machined to the desired shape from the rod, bar or tube stock to form a unitary finished product having superior qualities. However, the cost associated with directly forming or machining an end of the elongate metal member are relatively high. This is particularly true in the case of large products, such as sucker rods, which often exceed 30 feet in length. Handling of such products for machine or forging operations can be difficult and expensive.
Because of the difficulties involved in directly forging or machining the formed end products, a welding process is often used to attach a preformed end to the end of the elongate member. Welding processes particularly well suited for this application include friction welding, inertia welding, and flash butt welding. However, formation of a weld joint in the product often introduces a "weak link" which maybe unacceptable. Cleanliness of the steel, reorientation of weld metal, and heat affected zones produced by the welding process all may contribute to formation of a weld joint which directly or indirectly weakens the product. In corrosive environments, the joint will be attacked first due to flow line reorientation in the weld. Thus, the weld joint will become the starting point for stress corrosion failure.
In many applications which require a high degree of safety and reliability, introduction of weaknesses such as those described above is unacceptable. One solution to this problem is to increase the size (i.e., cross-section) of the elongate member and the formed end at the weld joint to increase the strength at this point. This can be accomplished by simply using an oversized elongate member and formed end. Alternatively, the end of the member can be upset (enlarged) in a forging operation to provide a weld joint which is at least as strong as the base material of the elongate member. However, utilization of either of these solutions is likely to seriously erode, or completely eradicate, the cost savings associated with the use of a welding process in fabricating the formed end products.
Accordingly, it is an object of this invention to provide an improved method and apparatus for the manufacture of formed end metal products.
Another object of this invention is to provide a method for the manufacture of formed end metal products in which a forging operation can be efficiently and economically employed to upset an end of an elongate metal member.
A still further object of this invention is to provide apparatus which allows an upset forging operation to be performed on an elongate metal member while the member is positioned in a welding apparatus.
Yet another object of this invention is to provide a method in which a welding apparatus can be used to perform an upset welding operation to enlarge the end of an elongate member.
These and other objects of the invention are achieved in a method of making a formed end metal product which comprises the steps of locating an elongate metal member in a first workholding means of a welding apparatus, locating a forging die in a second workholding means of the welding apparatus, upsetting an end of the elongate member by means of a compressive force developed by the welding apparatus, said force acting to press the forging die against the end of the member, locating a formed end in the second workholding means of the welding apparatus, and welding the formed end to the upset end of the elongate member. The end of the elongate member may be cold forged or, alternatively, hot forged by the welding apparatus. In the latter case, the end of the member is preferably heated by inductive heating means or by the passage of an electric current through the end of the member, while it is mounted in the workholding means of the welding apparatus. The end of the elongate member may alternatively be heated prior to locating the member in the first workholding means. The elongate member is preferably located in the first workholding means such that, subsequent to the forging step, the forged end of the elongate member extends beyond the die insert to facilitate the welding step. The forging die, the formed end, and the elongate member may be located in the welding apparatus by manual or by automatic loading means.
The apparatus required for making a formed end metal product, according to the method of present invention, comprises a welding apparatus having a first workholding means for holding the elongate metal member, a second workholding means, and means for developing a compressive force between the first and second workholding means. A forging die, adapted for mounting in the workholding means, forms a die cavity around the end of the elongate metal member. The end of the elongate metal member is forged into conformity with the die cavity by means of the compressive force developed by the welding apparatus. The forging die is preferably formed in two parts. A first die, adapted for mounting in the first workholding means, forms at least a portion of the die cavity around the end of the elongate member. A second die, adapted for mounting in the second workholding means, has a centralized depression which also forms a portion of the die cavity. The apparatus further comprises means for heating the end of the elongate member prior to the forging step. The heating means may comprise an inductive heating means or means for passing an electrical current through the end of the elongate member. Preferred welding apparatus for performing the method of the present invention include friction welders, inertial welders, and flash butt welders.
Additional objects and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment, when considered in conjunction with the accompanying drawings.